MWCNT and SiO2 Nanoparticle Enhanced Drilling Fluid Formulation and Characterization: Experimental and Simulation studies

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MSc Thesis, Afiya Akram, UiS 2018

FACULTY OF SCIENCE AND TECHNOLOGY

MASTER’S THESIS

Study programme/specialization:

Petroleum Engineering/ Drilling Technology

Spring/Autumn semester, 2018 Open

Author: Afiya Akram

………..

(Signature of author) Programme coordinator:

Supervisor(s): Mesfin Belayneh.

Muhammad Awais Ashfaq Alvi Title of master’s thesis:

MWCNT and SiO² Nanoparticle Enhanced Drilling Fluid Formulation and Characterization: Experimental and Simulation studies

Credits: 30

Keywords:

Drilling fluid

MWCNT nanoparticle Silica nanoparticle (SiO²) Rheological properties Tribology

Viscoelasticity

Number of pages: ………101…………

+ Supplemental material/other: 21…...

Stavanger, ………12-02-/2018…………

Date/year

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MSc Thesis, Afiya Akram, UiS 2018

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Afiya Akram, MSc Thesis, UiS, 2018 i

Dedication

This work is dedicated to the memory of my grandfather, M. Ellahi, who passed away during this thesis work. He was looking forward to read through this thesis.

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Afiya Akram, MSc Thesis, UiS, 2018 ii

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Afiya Akram, MSc Thesis, UiS, 2018 iii

Acknowledgements

First of all, I would thank God to give me the strength to complete this thesis.

I would like to express my sincere gratitude and appreciation to my supervisor Mesfin Belayneh for his knowledge, engagement and the endless support during this thesis work.

I am so thankful to have you as a supervisor, you pushed me and motivated me when I needed it the most. Thank you for always having the door open at your office. You are a really caring person, and I wish you all the best in the future. I would also like to thank my supervisor Awais Muhammed. Your help through this thesis is highly appreciated. I wish you the best in future to come.

Furthermore, I would like to thank University of Stavanger for letting me use their facilities for my laboratory work and simulation studies.

Finally I would thank my husband, Hamad, who has supported me to fulfil my dream. I would also thank my mother and father. Sincerely thanks to my mother who took care of my beautiful daughters, Sarina and Raya, while I studied. Also thanks to Sarina and Raya for being patient while mummy studied.

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Afiya Akram, MSc Thesis, UiS, 2018 iv

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Afiya Akram, MSc Thesis, UiS, 2018 v

Abstract

In recent years the application of nanotechnology has shown impressive results in improving the performance of drilling fluid, enhanced oil recovery and in cement.

However, the research and development based on nanotechnology in the oil industry are at its early stage. This indicates a huge research and development potential of nanotechnology in this field as well as application of this advance systems in industry.

In this thesis the effects of single (MWCNT, SiO²) and the composite (MWCNT-SiO²) nanoparticles on Carboxymethyl cellulose (CMC) and Xanthan gum (XG) based reference drilling fluids were tested. Based on the considered laboratory drilling fluids and the nanoparticle concentration, the overall results summarized as:

 0.38wt. % MWCNT nanoparticle reduced the friction coefficient of XG-base drilling fluid by 50%.

 0.0095wt. % SiO2 nanoparticle reduced the friction coefficient of XG-base drilling fluid by 25%.

 0.37wt. % SiO2 - 0.0095wt % MWCNT composite reduced the coefficient of friction of CMC base drilling fluid by 38%

 MWCNT and Silica nanoparticles increased the measured filtrate loss.

 Nanoparticle additives did not show a significant impact on plastic viscosity.

 The single MWCNT and Silica nanoparticles increased yield stress of base drilling fluid.

 Reduction of coefficient of friction reduced torque& drag.

 MWCNT nanoparticle treated drilling fluid showed improved hole-cleaning efficiency.

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Afiya Akram, MSc Thesis, UiS, 2018 vi

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Afiya Akram, MSc Thesis, UiS, 2018 vii

Table of content

DEDICATION ... I ACKNOWLEDGEMENTS ... III ABSTRACT ...V

1 INTRODUCTION ... 1

1.1BACKGROUND /MOTIVATION ... 1

1.2PROBLEM FORMULATION ... 3

1.3SCOPE AND OBJECTIVE ... 3

1.4RESEARCH METHODS ... 3

2 THEORY ... 5

2.1RHEOLOGY ... 5

2.2RHEOLOGICAL MODELS ... 8

2.2.1 Newtonian Model ...10

2.2.2 Non-Newtonian Models ...10

2.2VISCOELASTICITY ... 14

2.2.1 Oscillatory Amplitude Sweep Test ...17

2.4TORQUE AND DRAG ... 18

2.5HYDRAULICS ... 20

3 LITERATURE STUDY ... 25

3.1APPLICATION OF NANOPARTICLES IN THE OIL INDUSTRY ... 25

3.1.1 Drilling fluids ...25

3.1.2 Cement ...26

3.1.3 EOR ...27

3.2DESCRIPTION OF CHEMICALS USED IN THIS THESIS WORK ... 28

3.2.1 Bentonite ...28

3.2.2 Xanthan Gum-XG ...32

3.2.3 CMC ...32

3.2.4 KCl salt ...33

3.3NANOPARTICLES ... 33

3.3.1 MWCNT nanoparticle description ...33

3.3.2 Silica dioxide nanoparticle description ...34

4 EXPERIMENTAL WORK ... 37

4.1EFFECT OF MWCNT IN XG ... 37

4.1.1 Description and fluid formulation ...37

4.1.2 Characterization of MWNCT fluids ...38

4.1.2.1 Viscometer response and rheology parameters ...38

4.1.2.2 pH and filtrate loss...41

4.1.2.3 Tribometry coefficient of friction measurement ...41

4.2EFFECT OF SIO2 IN XG ... 44

4.2.2 Characterization of SiO2 fluids ...44

4.3EFFECT OF SIO2-MWCNT COMPOSITE EFFECT IN CMC ... 49

4.3.2 Characterization of SiO2-MWNCT fluids ...50

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Afiya Akram, MSc Thesis, UiS, 2018

4.4VISCOELASTICITY ... 55

4.4.1 Amplitude sweep measurement ...55

4.4.2 Flow point shear stresses comparisons ...57

5 PERFORMANCE SIMULATION ... 59

5.1RHEOLOGICAL MODELLING ... 59

5.1.1 Reference (XG) system ...59

5.1.2 Reference (XG) + 0.15g MWCNT ...61

5.1.3 Reference (XG) + 0.05g SiO2 ...62

5.1.4 Comparisons of model and measurement ...63

5.1.5 Effect of MWCNT and SiO2 on rheology parameters in XG system ...64

5.1.6 Effect of MWCNT and SiO2 mixture in CMC system ...66

5.2TORQUE AND DRAG SIMULATION ... 68

5.2.1Simulation setup ...68

5.2.2 Simulation result ...70

5.3.3 Summary of simulation ...73

5.3HYDRAULICS SIMULATION ... 74

5.3.1 Simulation Setup ...74

5.3.2 Simulation Result for XG Drilling Fluids ...74

5.3.3 Simulation Result for CMC Drilling Fluids ...77

5.4HOLE-CLEANING SIMULATION ... 79

5.4.1 Simulation setup ...79

5.4.2 Simulation results ...79

6 RESULT DISCUSSION AND SUMMARY ... 81

6.1RHEOLOGICAL EFFECTS OF NANO-TREATED DRILLING FLUIDS ... 81

6.1.1 Rheological Effects of MWCNT in XG ...81

6.1.2 Rheological Effects of Nano-silica in XG ...82

6.1.3 Rheological effects of Nano-silica-MWCNT Composite in CMC ...82

6.2FRICTIONAL EFFECTS OF NANO-TREATED DRILLING FLUIDS ... 82

6.3VISCOELASTIC EFFECTS OF NANO-TREATED DRILLING FLUIDS ... 83

6.4RHEOLOGICAL MODELLING OF NANO-TREATED DRILLING FLUIDS ... 83

6.5TORQUE AND DRAG EFFECTS OF NANO-TREATED DRILLING FLUIDS ... 84

6.6HYDRAULIC PERFORMANCE EFFECTS OF NANO-TREATED DRILLING FLUIDS ... 84

6.7HOLE CLEANING EFFECTS OF NANO-TREATED DRILLING FLUIDS ... 84

6.8SUMMARY MATRIX ... 85

7 CONCLUSION ... 87

8 REFERENCES ... 89

APPENDIX ... 92

APPENDIX A:WELL AND DRILL STRING PARAMETERS ... 92

APPENDIX B:WELL PATH PARAMETERS ... 93

APPENDIX C:AMPLITUDE SWEEP VISCOELASTICITY OF DRILLING FLUIDS ... 94

APPENDIX D:RESEARCH PAPER PRODUCED FROM THIS MSC WORK ... 97

LIST OF FIGURES ...105

LIST OF TABLES ...108

LIST OF SYMBOLS ...110

LIST OF ABBREVIATIONS ...112

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Afiya Akram, MSc Thesis, UiS 2018 1

1 Introduction

This thesis presents the formulation and characterization of nanoparticle-enhanced drilling fluids. Drilling fluid properties such as rheology, filtrate loss, lubricity and viscoelasticity were analyzed in this work. In addition, the performance of the drilling fluids was simulated with rheology models, torque and drag, hydraulics and hole-cleaning.

1.1 Background / Motivation

Drilling fluids are an essential part of the drilling operation. Drilling fluid is defined as a circulating fluid, used in rotary drilling operations to perform various functions [1]. The major functions of a drilling fluid are to transport cuttings to the surface, provide hydrostatic pressure, stabilizing the wellbore, and to cool and lubricate the drill bit [2]. A properly designed drilling fluid is very important to achieve success in the drilling operation [3]. One of the main consideration when designing a drilling fluid is to keep the well cost to a minimum [2]. Figure 1.1 shows a typical drilling and fluid circulation system [4].

Figure 1.1: Drilling system [4]

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The two commonly used drilling fluids in the oil industry are water based mud (WBM) and oil based mud (OBM). WBM is environmental friendly and cheaper.

However, poorly designed WBM easily interact with clay minerals in shale which led to clay swelling. On the other hand, OBM gives good wellbore stability and lubricity properties as it minimizes the interaction with shale [5]. Moreover, OBM has a higher rate of penetration (ROP) and lower coefficient of friction compared to the WBM. However, OBM is very costly and has a negative impact on the environment due to spills and disposal [6].

The world’s population is increasing, and so is the demand for energy, while the tendency of finding oil and gas easily is decreasing [7]. Hence, the oil industry is shifting towards higher risks and extremely challenging drilling environments such as extreme water depths, high pressure high temperature (HPHT) formations and complex geological formations. Drilling in these harsh environments requires new tools, equipment and technology, which have better technical performance than the conventional drilling methods.

The application of nanotechnology (1-100nm) is successfully proven in several industries such as electronic, material composites, medical and even consumer goodsas well [8]. Recent research has shown an improved performance of nanotechnology in petroleum engineering, such as in drilling fluids, enhanced oil recovery (EOR) and cementing [9].

In this thesis the effect of single and composite nanoparticles in bentonite WBM will be investigated. Drilling fluids were designed both with and without nanoparticles to compare the nanoparticle drilling fluid with the conventional drilling fluid system. The drilling fluid systems were formulated with various concentrations of nanoparticles in order to check the effect of different concentrations of the particles on the properties of drilling fluid. The fluid rheology, pH, filtrate loss and friction coefficient were investigated, and the best system was selected to study the viscoelasticity of the fluids. At the end, a simulation study was performed to investigate the effect of nanoparticles further.

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1.2 Problem formulation

The main issues to be addressed in this work are:

• Single effect of MWCNT and SiO2 nanoparticles in the conventional drilling fluids

• Combined effect of MWCNT and SiO² nanoparticles in the conventional drilling fluids

1.3 Scope and Objective

The primary objectives of this thesis are to formulate and characterize nanoparticle- based drilling fluids. In addition, to perform simulation studies such as torque and drag, hydraulics and hole-cleaning.

1.4 Research methods

Figure 1.2 illustrates the summary of the thesis work. As shown, the thesis is divided into three main topics. Part 1 describes theories used for the evaluation of the drilling fluid, literature study deals with the review of the application of nanoparticles in drilling fluids and description of the drilling fluid ingredients. Part 2 contains experimental work, which deals with the drilling fluids formulation and characterization. Whereas, part 3 deals with the performance simulation studies.

Figure 1.2: Research methods MSc Thesis work

Literature study

Theory

Application of nanoparticles Drilling fluid

ingredients

Experimental

Rheology Tribology Viscoelasticity

Simulation

Rheological modelling Torque and drag Hydraulics

Hole cleaning

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2 Theory

This chapter reviews the relevant theories, which are being used for the analysis of experimental results obtained in chapter 4 as well as for the performance simulation studies in chapter 5. The theories are presented for the rheology, viscoelasticity, torque and drag and hydraulic.

2.1 Rheology

Rheology deals with the science of deformation and flow [10]. It is important to understand the rheological properties of the drilling fluid as the rheological properties directly affect the flow characterization and hydraulic calculations [11].

Drilling fluid has several functions, and the fluid rheology must be controlled in order to perform these functions in an optimal way [12].

The drilling fluid rheology also plays a key role during the drilling process. The rheology parameters are being used to describe the drilling fluid in different conditions, in order to design an optimum circulating system. The rheology of the drilling fluids are used in the following determinations [11]:

• To calculate the friction loss in the annulus and pipes

• To estimate ECD of the drilling fluid

• To determine the flow regime in the annulus

• To estimate the hole cleaning efficiency

• To evaluate the capacity of fluid suspension (surge and swab pressures)

• To calculate the settling velocity for cuttings

There are several basic concepts in rheology to describe the behaviour/properties of the fluids, the concepts are defined in the sections below.

Reynolds number and Flow regimes:

Reynolds number is a dimensionless number which is defined by the fluid`s inertial forces and the viscous forces.. The Reynolds numbers are used to indicate the flow regime of fluid. Figure 2.1 illustrates the three flow regimes, which are laminar, transitional and turbulent.

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In laminar flow, the fluid is moving in parallel to the wall in straight and smooth lines. The fluid velocity increases from zero near the wall, to a maximum value in the middle of the pipe. The velocity profile has a parabolic profile. Generally, slowly moving fluids or viscous fluids are categorized to have laminar flow. The Reynolds number for laminar flow is lower than 2000.

The turbulent flow is recognised as when the flow pattern of the fluid is unsorted and chaotic. Turbulent flow occurs for higher velocities or for fluids with low viscosities. The Reynolds number for turbulent flow is greater than 4000.

Transition flow is a state between the laminar flow and turbulent flow. It is when the flow pattern changes from uniform to unsorted and chaotic movements. The Reynolds number for transition flow is between the range of 2000 and 4000.

Laminar Transitional Turbulent Figure 2.1: Illustration of fluid flow patterns

Viscosity:

Viscosity is a term which describes fluid`s flow resistance. Resistance to flow occurs due to the internal forces, like mechanical, friction and electrostatic forces between the molecules. Viscosity is defined as a relation between shear stress and shear rate.

The shear stress of a fluid is the ratio of shear force and the shear area, while the shear rate is given by the ratio of velocity and the distance. The value of viscosity is not constant for most of the drilling fluids, the viscosity changes as the shear rate changes, therefore the shear stress is measured at different shear rates to fully understand the viscosity behaviour of the fluid. The viscosity is also dependent on the pressure, temperature and time.

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Plastic Viscosity (PV):

The plastic viscosity describes the drilling fluid`s flow resistance which occurs due to the mechanical friction between the particle-particle, particles-fluid and fluid- fluid. The value of PV is dependent on the concentration, size and shape of the additives in the drilling fluid, as well on the viscosity of the fluid. The PV is determined by using 600RPM and 300RPM Fann viscometer and is given by [12]:

PV= Q600- Q300 1

Where:

• Q⁶⁰⁰= Fann viscometer reading at 600 RPM shear rate

• Q300=Fann viscometer reading at 300RPM shear rate

Yield Stress (YS):

The yield stress describes the drilling fluid´s flow resistance which occurs due to the electrostatic and chemical forces between the particles in the fluid. A higher YS indicates stronger internal molecular forces within the drilling fluid. To initiate flow, the pressure should exceed the shear yield stress. The YS can be calculated from Fann data as [12]:

YS= 2Q300- Q600 2

Gel-strength (gel):

Gel strength gives a measurement of the electrical attractive forces within the particles in the drilling fluids. Both gel strength and yield stress parameters are influenced by the internal forces between the particles.

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2.2 Rheological Models

Several mathematical models have been developed to characterize the fluid flow by the rheological parameters. These models relate shear stress with the shear rate. By using the measured data and the models, it is possible to determine viscosity and gel strength of the drilling fluid. These two parameters are important in order to describe the performance of the drilling fluid, such as efficiency of cutting transport and pressure calculations.

Drilling fluids are very complex fluids. Selection of the best rheological model is based on the comparison between the measured and calculated shear stresses and shear rates. The rheological models can be categorized as Newtonian and non- Newtonian. For the Newtonian model, the viscosity remains constant with the change in shear rates. The viscosity for non-Newtonian models varies with the change in shear rates. Some of the rheological models are illustrated in figure 2.2.

Figure 2.2: Illustration of shear stress-shear rate behavior of fluids [13]

In the following section, an example will be shown on how to transform data from the Fann viscometer into shear stresses and shear rates. A set of viscometer data from the experimental study and transformed data are presented in table 2.1.

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To transform the RPM values and corresponding viscometer readings into shear stresses and shear rates following conversion factors has been applied [14]:

γ=1.703*RPM 3

τ=1.063.Reading 4

Table 2.1: Illustration of viscometer data and field unit transformed data

Figure 2.3: Photograph picture of Fann 35 viscometer

RPM Reading

θ600 39

θ300 32

θ200 29

θ100 24

θ6 15

θ3 11

γ (s^-1) τ(lbf/100sqft)

1022 42

511 34

341 31

170 26

10 16

5 12

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2.2.1 Newtonian Model

A fluid is characterized as Newtonian if the shear stress is directly proportional with the shear rate, with the viscosity as the proportionality constant. The graphical relation between the shear stress and the shear rate is a straight line, which passes through the origin. Water is an example of a Newtonian fluid, where the viscosity does not change as the shear rate change. The equation for the Newtonian model is given by [14]:

τ= µγ 5

Where:

• τ=shear stress

• µ=viscosity

• γ=shear rate

Using measured data and equation 5, from the slope of the line, the viscosity can be estimated by using the following equation [14]:

µ (cP)=47880*slope/100 6

2.2.2 Non-Newtonian Models

For most of the drilling fluids, the Newtonian model does not apply to them. Most of the drilling fluids are non-Newtonian, the non-Newtonian models characterize the fluids by two or more parameters.

2.2.2.1 Bingham Plastic Model

The Bingham Plastic model is the most common rheological model used for the drilling fluids. It is a two parameters model. The shear stress and shear rate relation

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are linear as in case of Newtonian model. The equation for Bingham plastic model is given by [14]:

τ= YS +µpγ 7

Where:

• YS =Yield stress

• µ_p (PV)=Plastic viscosity

Yield stress and plastic viscosity can be calculated using the Fann viscometer data and equations 1 and 2.

2.2.2.2 Power-law Model

As for Bingham plastic model, Power-law model also characterizes the fluid by using two parameters. The graphical relation for shear stress and shear rate is represented by a straight line in a log-log graph. The Power-law model is represented by the following equation [14]:

τ = kγⁿ 8

Where:

• k= Consistency index (lbf/100sqft)

• n= Flow behavior index []

The parameters k and n can be calculated by using the following equations [14]:



 



= 

300

log 600

32 .

3 θ

n θ 9

k n

511 θ300

= 10

Graphically, the value of n represents the slope of the straight line, and the value of k represents the intercept at γ=1.

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The flow behavior index (n) represents the type of fluid, hence the Power-law model can be used to represent more than one type of fluid, when:

• n<1 it is a pseudoplastic fluid

• n=1 it is a Newtonian fluid

• n>1 it is a dilatant fluid

When the n-value is below one, the fluid is called a shear thinning fluid, which means that the viscosity decreases as the shear rate increases. Most of the drilling fluids show shear thinning behavior. When the n-value is greater than one, the fluid is dilatant. The viscosity of dilatant fluid increases as the shear rate increases. This behavior is not shown by drilling fluids.

2.2.2.3 Herschel Bulkley Model

Herschel Bulkley’s model characterizes a fluid by three parameters. The model is given by [14]:

τ= τo +Κγⁿ 11

Where:

• τo =Yield point

• K= Consistency index

• n= Flow behavior index

The Herschel Bulkley model is a modified Power-law model. In this model, yield stress is included. This model describes the rheological behavior of drilling fluid.

The n-value and k-value can be found graphically. τo can be calculated by using the following equation [14]:

min max

*

min max 2

*

τ τ τ

τ τ τ τ

−

= −

o 12

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Where, τmax and τmin are the maximum and minimum measured shear stresses. The shear stress,^τ^*, is determined by interpolation from the corresponding geometric mean of the shear rate max min ¹

* = γ γ =72.25s⁻

γ , which is between the Q⁶ and Q¹⁰⁰.

2.2.2.4 Unified Model

The unified model is a simplified version of Herschel Bulkley model. This model involves the parameters k and n as in the case of Herschel Bulkley model, but instead of τ_o, a new parameter is introduced, that is τ_y, a lower shear yield point. The lower shear yield is derived from the Fann viscometer readings at 6 RPM and 3RPM. The Unified model is described by [14]:

τ= τy +Κγⁿ 13

Where:

• τy(lbf/100sqft) =1.066∗(2Q³- Q⁶) 14 2.2.2.5 Robertson and Stiff Model

The Robertson and Stiff model is shown to be superior to Bingham and Power-law model, but has not gained recognition in the drilling industry because of its complexity. The model can be represented by the following equation [14]:

τ=Α(γ+C)^B 15

Where:

A, B and C are the parameters of the Robertson and Stiff model. A and B parameters are similar to the parameters k and n of the Power-law model. The parameter C is the correction factor to the shear rate, and the term (γ+C) represents the effective shear rate. The parameter C is given by [14]:

min max

*

2

* min max

2γ γ γ

γ γ γ

−

= −

C 16

Where:

γ*is calculated by interpolation of the corresponding geometrical shear stress, given as: max min

* τ τ

τ = 17

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2.2 Viscoelasticity

Viscoelastic behavior is shown by the materials having both fluids and solids.

Drilling fluids exhibit viscoelastic behavior, which means that they can be characterized with respect to viscous and elastic behavior under deformation.

Viscoelastic properties are time-dependent, where viscosity decreases or increases with a change in shear stress or shear rate. Viscosity increases with time when higher shear stress is applied, however higher shear stress can also lead to viscous heating, which can decrease the viscosity. Hence, viscosity can also be decreased with the increase in the shear rates. The elastic property of the drilling fluids stores energy when deformation is applied and has great effect on the behavior of flow and pressure drop. The viscoelastic properties play very important role in order to evaluate the structure and strength of gel, barite sag, hydraulic modelling and solid suspension [15]. Viscosity is not the only parameter which can define the behavior of the drilling fluids. Even though the viscous components are dominating factor in common operations. Even when infinitesimal deformation is applied on the drilling fluids, the response of the applied deformation provides viscoelastic response, as indicated by the gel structure. Gel structure formation is one of the many requirements which the drilling fluid has to fulfill. Gel structure formation is important in order to transport cuttings and to keep the cuttings floating while the circulation stops. The viscoelastic response of the drilling fluids can be determined by performing oscillatory tests with the rheometer shown in figure 2.4.

The basic principle behind the oscillatory tests can be explained by using Two- Plates-Model, illustrated in figure 2.5. The drilling fluid sample is placed between two plates, where the bottom plate is stationary and the upper plate has oscillatory movements. The movement of the upper plate induces shear in the fluid sample [10].

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Figure 2.4:Photograph picture of Anton Paar MCR 302 rheometer

Figure 2.5: Illustration of the two-plate-model oscillatory test [16]

During the oscillatory tests, the fluid sample is exposed to varying sinusoidal deformation (strain) and the resulting stress is measured. Figure 2.6 shows the stress and strain response as a function of time, the phase angle and amplitude is also illustrated.

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Figure 2.6: Stress strain response for an oscillatory measurement of a viscoelastic material [16]

The applied shear strain (γ) and the measured shear stress (τ) are defined as [15]:

𝛾𝛾(𝑡𝑡) =𝛾𝛾𝑜𝑜sin(𝜔𝜔𝑡𝑡) 18

𝜏𝜏(𝑡𝑡) =𝜏𝜏𝑜𝑜sin(𝜔𝜔𝑡𝑡+𝛿𝛿) 19

𝜏𝜏(𝑡𝑡) =𝜏𝜏𝑜𝑜[sin(𝜔𝜔𝑡𝑡)𝑐𝑐𝑐𝑐𝑐𝑐𝛿𝛿+ cos(𝜔𝜔𝑡𝑡)𝑐𝑐𝑠𝑠𝑠𝑠𝛿𝛿] 20

𝜏𝜏(𝑡𝑡) =𝛾𝛾₀��^𝜏𝜏_𝛾𝛾^𝑜𝑜

0𝑐𝑐𝑐𝑐𝑐𝑐𝛿𝛿�sin(𝜔𝜔𝑡𝑡) +�^𝜏𝜏_𝛾𝛾^𝑜𝑜

0𝑐𝑐𝑠𝑠𝑠𝑠𝛿𝛿�cos(𝜔𝜔𝑡𝑡)� 21

𝜏𝜏(𝑡𝑡) =𝛾𝛾₀[𝐺𝐺^′sin(𝜔𝜔𝑡𝑡) +𝐺𝐺^′′cos(𝜔𝜔𝑡𝑡)] 22

The Storage Modulus and Loss modulus are defined by following equations [15]:

𝐺𝐺^′= �^𝜏𝜏_𝛾𝛾^𝑜𝑜

0𝑐𝑐𝑐𝑐𝑐𝑐𝛿𝛿� 23

𝐺𝐺^′′ =�^𝜏𝜏_𝛾𝛾^𝑜𝑜

0𝑐𝑐𝑠𝑠𝑠𝑠𝛿𝛿� 24

The damping factor, also called loss factor, is the ratio of the lost and the stored energy, caused by the deformation, and is given as:

𝑡𝑡𝑡𝑡𝑠𝑠𝛿𝛿= �^𝐺𝐺_𝐺𝐺^′′_′� 25

𝛿𝛿=𝑡𝑡𝑡𝑡𝑠𝑠⁻¹�^𝐺𝐺_𝐺𝐺^′′_′� 26

Where 𝛿𝛿 is the phase angle, this parameter describes where the phase changes occur for the fluids. The phase angle is equal to 90⁰ for an ideally viscous fluid, in

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this case the Loss Modulus completely dominates the Storage Modulus. For the ideally elastic fluid the phase angle is equal to zero and for this case Storage Modulus dominates the Loss Modulus. When the phase angle is 45^o, the Storage Modulus is equal to the Loss Modulus, and the fluid then comprises of 50 percent viscous portion and 50 percent elastic portion and is at the transition point. This point is also called the flow point. The viscoelastic materials have phase angle values between 0 and 90. The viscoelastic parameters are presented schematically in table 2.2.

Phase angle 0 < 𝛿𝛿< 45 𝛿𝛿 = 45 45 <𝛿𝛿< 90

Behaviour Elastic dominated Transitional Viscous dominated

G’ and G’’ G’ > G’’ G’ = G’’ G’ < G’’

Table 2.2: Classification of materials from oscillatory tests [10]

2.2.1 Oscillatory Amplitude Sweep Test

An oscillatory sweep test is performed at a variable amplitude of oscillation, while the frequency is held constant. The measuring temperature of the sample fluid is also kept constant. When a small strain is applied to the fluid sample, the sample will undergo a deformation while the internal structure of the fluid remains unchanged.

The Storage and Loss Modulus will have constant values at different levels, and are presented as a linear horizontal range on the graph, called linear viscoelastic range (LVER). LVER is obtained at low amplitude values. A higher strain is further applied on the fluid sample, until it reaches a critical value where the internal structure of the fluid sample is irreversibly deformed and LVER changes into a nonlinear viscoelastic range. The flow point and yield point can be determined from the curves that are based on the data from the amplitude sweep tests. The flow point is the point where the fluid starts to flow, and can be found by taking the value at which Storage Modulus curve and Loss Modulus curve meets, at this point the phase angle is 45⁰ and the system is equally balanced with respect to viscosity and elasticity. In the LVER the fluid sample exhibits gel-like character, after the flow point the fluid sample becomes more viscous. The yield point can be found at the limit of the LVER,

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where the linearity of the Storage Modulus and Loss Modulus starts to deviate from horizontal plateau. The LVER, flow point and yield point are illustrated in figure 2.7.

Figure 2.7: Right: Strain amplitude sweeps showing gel-like character. Left: Stress amplitude showing yield point and flow point [10]

2.4 Torque and Drag

Figure 2.8 shows a drill string which is divided into small segments. The axial load transfer in the drilling string during tripping is given as the vectors sum of loadings in the axial direction, which are static weight and friction-drag force. As illustrated in figure 2.8, the small element ds is loaded with axial loads and torque. The force at the top is computed by using (Johancsik et al. 1989) [17]:

(

s e

) (

e

)

s L

i

i F w ds Fd F d w ds dF

F₊₁ = ±µ β sinθ − θ ² + sinθ ϕ ²+β cosθ + 27

Where, µ is coefficient of friction, w is weight per unit length, θ and ϕ are well inclination and azimuth, respectively.

As shown in the equation 27, lower coefficient of friction provides better drag reduction, which allows to drill a longer offset. This can be done by improving the lubricity of drilling fluid. Therefore, this thesis work is designed for this purpose.

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Figure 2.8: Segmented drill string and loads [13]

dFL in equation 27 is the fluid flow effect on drill string, which is a function of flow rate.

Maidla and Wojtanowicz (1987) [18] also derived the effect of viscous pressure gradient on each pipe element. The hydrodynamic viscous drag force, which is combined with the drag equation, is given as dynamic viscous drag force, which is to be coupled with the drag equation, is given as:

2

4 1 ⁱ ⁱ

n

i

fl sd

ds

F P∆



 



=

∑

 ∆

=

π 28

Where, the pressure loss term with fluid velocity and density in the annulus is given as:

d D

V f ds

P _av

= −

∆ ρ ²

29

Where:

• D = well diameter and d = outer diameter of the drill string

Drill string

∆s

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The friction factor, f, calculated based on the flow regimes, as shown in the table 2.3.

For laminar For turbulent,

Re

16

f = N 30 ₀_.₂₅

Re

0791 . 0

f = N 31

n n an

n x n d D k x V

N 



 





+

= ⁻ −

1 2 10 48

9 . 10

2 4 Re

ρ 32

For laminar flow: N^Re ≤ 3470 -1370xn & For turbulent flow: N^Re ≥ 420 -1370xn Table 2.3: Friction factor for laminar and turbulent flow [18, 19]

Where:

• N^Re is the Reynolds number

• n is flow-behavior index

• k is consistency index dyne.s/100 cm² 2.2 Torque

Aadnøy et al. (2009) also derived a three-dimensional model in a curved section given as [19]:

rN

T =µ 33

Where, µ is the coefficient of friction, r is the radius of the drill string, and N is contact force. Drilling fluid with higher lubricity reduces the torque, which is suitable for the drilling operation. This thesis will investigate the effect of nanoparticles on the lubricity of drilling fluid.

2.5 Hydraulics

Hydraulics deals with the determination of pressures when drilling fluid circulates.

Drilling fluid is pumped through the circulation system by mud pump. During circulation process, as illustrated in figure 2.9, friction pressure losses occur in the different part of the circulation system. Pressure losses prediction is important for [2]:

• Drill bit hydraulic program design

• ECD during tripping in and tripping out operations

• ECD during drilling and well control operations

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The Equivalent Circulating Density (ECD) describes the density of the drilling fluid when the friction loss while circulating is taken into account. ECD is given by [12]:

TVD g

ECD

_st

P

^annulus

. + ∆

= ρ

34

Where:

• ρ_st= Static mud density

• ∆P= Pressure loss in annulus

• TVD= True vertical depth

During tripping out operation, well pressure in the annulus will decrease. This is called swab pressure and can lead to kick. Likewise, when tripping in operation, an increase in annular pressure (also called surge pressure) may cause formation fracture. Therefore, it is important to analyze hydraulics in the wellbore in order to determine accurate well pressure.

Figure 2.9 illustrates the different components of frictional losses in a circulating system. The pump pressure is given as the sum of pressure losses in circulation systems [14]:

PP= ∆Ps + ∆Pdp+ ∆Pdc + ∆Padp + ∆Padc +∆Pb 35 Where,

• ∆Ps = Pressure loss at surface equipment

• ∆Pdp = Pressure loss inside of drill string

• ∆Pdc = Pressure loss inside of drill collar

• ∆Padp = Pressure loss in annulus (drill pipe/well or casing)

• ∆Padc = Pressure loss in annulus (drill collar/well)

• ∆Pb = Pressure loss across the drill bit

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Figure 2.9: Friction pressure losses during circulation [14]

Several hydraulics models are available in the literature. Since the Unified hydraulics model [20] includes both Bingham plastic and Power-law parameter, in this thesis Unified hydraulic modelwas selected for the analysis of pump pressure and equivalent circulation density (ECD) of drilling fluids to be formulated in Chapter 4. Sadigov [21] has also analyzed the model with the field and experimental data and he as reported the good prediction of the model. A summary of Unified hydraulics model used in chapter 5 for hydraulic calculations is presented in table 2.4.

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Pipe Flow Annular Flow

𝜇𝜇𝑝𝑝[𝑐𝑐𝑐𝑐] =θ600− θ300 𝜏𝜏𝑦𝑦 = θ300− 𝜇𝜇𝑝𝑝 𝜏𝜏0 = 1.066(2θ300− θ600) np = 3.32 log �^2𝜇𝜇_𝜇𝜇^𝑝𝑝^{+ 𝜏𝜏}^𝑦𝑦

𝑝𝑝 + 𝜏𝜏_𝑦𝑦� kp =1.066 �^𝜇𝜇^𝑝𝑝₅₁₁^{+ 𝜏𝜏}^𝑦𝑦�

np = 3.32 log �^2𝜇𝜇_𝜇𝜇^𝑝𝑝^{+ 𝜏𝜏}^{𝑦𝑦 −}^{𝜏𝜏𝑦𝑦}

𝑝𝑝 + 𝜏𝜏_𝑦𝑦−𝜏𝜏_𝑦𝑦 � k^p =1.066 �^𝜇𝜇^𝑝𝑝^{+ 𝜏𝜏}₅₁₁^𝑦𝑦^{− 𝜏𝜏}^𝑜𝑜�

G = �^{(3−𝛼𝛼)𝑛𝑛+1}_{(4−𝛼𝛼)𝑛𝑛} � �1 +^𝛼𝛼₂� α= 1 for annular, α= 1 for pipe

𝑣𝑣_𝑝𝑝[ 𝑓𝑓𝑡𝑡

𝑚𝑚𝑠𝑠𝑠𝑠] =24.51 𝑞𝑞

𝐷𝐷_𝑃𝑃² 𝑣𝑣𝑎𝑎[ 𝑓𝑓𝑡𝑡

𝑚𝑚𝑠𝑠𝑠𝑠] = 24.51 𝑞𝑞 𝐷𝐷₂²− 𝐷𝐷₁² γw [1/sec ]= ^{1.6∗𝐺𝐺∗𝑣𝑣}_𝐷𝐷

𝑅𝑅 𝜏𝜏𝑤𝑤 = ��^{4− 𝛼𝛼}_{3 – 𝛼𝛼}�� 𝜏𝜏0 + 𝑘𝑘 𝛾𝛾𝑤𝑤𝑠𝑠 𝑁𝑁𝑅𝑅𝑅𝑅 = 𝜌𝜌 𝑣𝑣_𝑝𝑝

19.36𝜏𝜏𝑤𝑤

𝑁𝑁𝑅𝑅𝑅𝑅 = 𝜌𝜌 𝑣𝑣_𝑅𝑅 19.36𝜏𝜏_𝑤𝑤 Laminar: 𝑓𝑓𝑙𝑙𝑎𝑎𝑙𝑙𝑙𝑙𝑛𝑛𝑎𝑎𝑙𝑙 = _𝑁𝑁¹⁶

𝑅𝑅𝑅𝑅

Transient: 𝑓𝑓𝑡𝑡𝑙𝑙𝑎𝑎𝑛𝑛𝑡𝑡𝑙𝑙𝑅𝑅𝑛𝑛𝑡𝑡 =

16 𝑁𝑁_{𝑅𝑅𝑅𝑅} (3470−1370𝑛𝑛_𝑝𝑝)

Turbulent: a = 𝑙𝑙𝑜𝑜𝑙𝑙 𝑛𝑛+3.93

50 } fturbulent = 𝑎𝑎

b = 1.75−𝑙𝑙𝑜𝑜𝑙𝑙𝑛𝑛 𝑁𝑁

7 }

Laminar: 𝑓𝑓𝑙𝑙𝑎𝑎𝑙𝑙𝑙𝑙𝑛𝑛𝑎𝑎𝑙𝑙 =_𝑁𝑁²⁴

𝑅𝑅𝑅𝑅

Transient: 𝑓𝑓𝑡𝑡𝑙𝑙𝑎𝑎𝑛𝑛𝑡𝑡𝑙𝑙𝑅𝑅𝑛𝑛𝑡𝑡 =

16 𝑁𝑁_{𝑅𝑅𝑅𝑅} (3470−1370𝑛𝑛_𝑝𝑝)

Turbulent: a = 𝑙𝑙𝑜𝑜𝑙𝑙 𝑛𝑛+3.93

50 } fturbulent = 𝑎𝑎

b = 1.75−𝑙𝑙𝑜𝑜𝑙𝑙𝑛𝑛 𝑁𝑁

7 }

f^partial= (ftransient-8 + fturbulent-8)^-1/8

f^p= (f^partial12 + f^laminar12)^1/12 fa = (fpartial12 + flaminar12)^1/12

�𝑑𝑑𝑑𝑑 𝑑𝑑𝑑𝑑�[𝑑𝑑𝑐𝑐𝑠𝑠

𝑓𝑓𝑡𝑡] = 1.076𝑓𝑓𝑝𝑝𝑣𝑣𝑝𝑝2𝜌𝜌 10⁵𝐷𝐷_𝑝𝑝

∆𝑑𝑑[𝑑𝑑𝑐𝑐𝑠𝑠] =�𝑑𝑑𝑑𝑑 𝑑𝑑𝑑𝑑� ∆𝑑𝑑

�𝑑𝑑𝑑𝑑 𝑑𝑑𝑑𝑑� �

𝑑𝑑𝑐𝑐𝑠𝑠

𝑓𝑓𝑡𝑡 �= 1.076 𝑓𝑓_𝑎𝑎𝑣𝑣_𝑎𝑎²𝜌𝜌 10⁵(𝐷𝐷₂ − 𝐷𝐷₁)

∆𝑑𝑑[𝑑𝑑𝑐𝑐𝑠𝑠] =�𝑑𝑑𝑑𝑑 𝑑𝑑𝑑𝑑� ∆𝑑𝑑

∆𝑑𝑑𝑁𝑁𝑜𝑜𝑁𝑁𝑁𝑁𝑙𝑙𝑅𝑅𝑡𝑡[𝑑𝑑𝑐𝑐𝑠𝑠] = 156𝜌𝜌𝑞𝑞²

�𝐷𝐷_𝑁𝑁1²+𝐷𝐷_𝑁𝑁2²+𝐷𝐷_𝑁𝑁3²�²

Table 2.4: Summary of the equations used in the Unified model [14]

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3 Literature study

This chapter presents the review of nanoparticles application in the oil industry and the description of chemical ingredients used to formulate the drilling fluids this thesis work.

3.1 Application of nanoparticles in the oil industry

As mentioned initially, nanotechnology has been successfully applied to numerous fields such as electronics, medical, painting and coating industry, cosmetics, the oil industry and many more. In the oil industry nanotechnology has been applied to drilling fluids, cementing and EOR. In the following sections some of the results from nanotechnology application in the drilling fluids, cement and EOR will be presented.

3.1.1 Drilling fluids

Sharma M. M. et al. (2012) [22] presented a paper where they have tested water based drilling fluids containing silica nanoparticle with 20-nm diameter silica spheres, and evaluated its interaction with shales. The tests were conducted to get details about the rheology and stability of the nanoparticle-treated drilling fluids, and to quantify the extent of water invasion into shales. Transient-flow test, also called pressure penetration test, were performed on the samples, which determined the physical plugging on the shales. Permeability changes for the nanoparticle enhanced fluids were compared to the same shale sample, and were used as an indicator of physical plugging. The results showed that the WBM having silica nanoparticle reduced the invasion into the shale by 10 to 100 times, which indicates that a good wellbore stability is obtained by using silica nanoparticles in drilling fluids. Another test result showed that silica nanoparticle effectively plugged pores in shales without micro-cracks, but could not alone plug the micro-cracks, at least not with this nanoparticle particle size and concentration.

Sedaghatzadeh M. et al. (2012) [23] studied the thermal and rheological effects of bentonite WBM with MWCNT as an additive. The thermal effects of the sample

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drilling fluids were measured by the transient hotwire (THW) method which determined the thermal conductivity of the materials. The thermal conductivity enhanced by 23.2% by adding 1 vol% of MWCNT at room temperature, by increasing the temperature to 50^oC, the thermal conductivity was increased by 31.8%. In addition, the rheological properties also showed significant improvements.

Li G. et al. (2012) [24] studied the effect of nanoparticles enhanced drilling fluids on the sealing ability for shale with micro-cracks. In order to form an appropriate mud cake with very low filtration, there must be a match between pore throat size and the particle size. The rheology and filtration effects were determined. Further, cake strength tests, pressure transmission tests and sound wave propagation speed tests were performed to verify sealing properties of the mud cake and permeability effects of the nanoparticles. The conventional sized calcium carbonate particles were compared with nano-sized calcium carbonate. The results of the test showed that conventional sized calcium carbonates could not effectively plug the small pore throats. The pressure transmission test showed that pressure transmission of shale decreased and coefficient of shear strength had increased after nanoparticles were added, which indicates that adding nano-sized material into the drilling fluid seals the pores of the shale. The concentration of nanoparticle used for this evaluation was 3%.

3.1.2 Cement

Baig M.T. et al. (2017) [25] studied the effect of various concentrations of nano- zeolite mixed with API Class G cement. Compressive strength was measured by ultrasonic cement analyzer (UCA) under HPHT conditions, porosity and permeability were analyzed in an automated permeameter/porosimeter, and finally the structure was examined by use of SEM. The results showed that by adding nano- zeolite into the cement, the strength development process was accelerated. During well-cementing operations, there are three important parameters, 50-, 500- and 2000psi compressive strength, and it is important to determine how much time it

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takes to achieve these strengths. By adding 2% nano-zeolite, the time to reach 2000psi strength was reduced by almost 30%, which means the wait-on-cement (WOC) time can be reduced by adding nanoparticle additives. The permeability and porosity also reduced significantly by the addition of 1% nano-zeolite, 98% and 17%

respectively.

3.1.3 EOR

Moradi B. et al. (2015) [26] studied the effect of silica nanoparticle on EOR. Water alternating gas (WAG) is one of the methods used to improve oil recovery, in this study the improvement of the WAG method by adding silica nanoparticles (Nano- WAG) into the aqueous phase was investigated. Silica nanoparticles powder with nanoparticle size of 11.14 nm, medium crude oil sample and plugs from a mature oil field in the Middle East was used for the experiments. Core-flooding experiments, IFT measurements and wettability measurements were performed. IFT measurements measured the interfacial force between oil and water and oil and the nano-fluid, by using Du Nouy ring method. During all experiments, the temperature was held 122^o F and the initial pressure at 800psi. The rate of injection was 8cc/hr and 15cc/hr for water/nano-water and gas, respectively. The results showed more than 20% incremental in recovery factor by adding nanoparticles in the conventional WAG process. The study also showed that silica nanoparticle adsorption changed the wettability of the rock from oil-wet to strongly water-wet, a property which affects the recovery. IFT also reduced by adding silica nanoparticle.

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3.2 Description of chemicals used in this thesis work 3.2.1 Bentonite

Clay is involved in two different scenarios during the drilling process, one during drilling in shale formations and one by using bentonite as an additive in the drilling fluids. The main component of WBM is clay, mostly bentonite [27]. Bentonite is added into the WBM as a viscosifier and to control filter loss. In this thesis the bentonite clay is used as an additive in the drilling fluids. The term bentonite was first used to describe the plastic clay found near the Fort Benton in Wyoming in the US [28]. Bentonite is defined as a clay, which may have volcanic or non-volcanic origin, consisting of smectite group minerals [29]. Smectite was earlier referred as montmorillonite, and the term is still being used in the oil industry [12].

Montmorillonite is the dominating mineral in the bentonite, bentonite can also contain other clay minerals, like illites and kaolinites. Non-clay minerals can comprise 10-30 percent of the total amount of bentonite [12]. The unique properties obtained by bentonite in the drilling fluids, like clay swelling and thixotropic qualities, are due to the montmorillonite minerals. The chemical composition of the commercial bentonites is presented in table 3.1.

Table 3.1: Composition of commercial bentonite [28]

Bentonite can be classified into two categories, depending on the swelling abilities in the water. Sodium (Na+) bentonite exhibits higher swelling capability, called

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osmotic swelling, this swelling is caused by the water that comes between the unit layers in the clay structure due to the higher concentration of cations between the unit layers than the cations in the surrounding water [1]. Whereas, bentonite with calcium (Ca++) ions exhibits a lower swelling ability, called surface hydration. This type of swelling occurs when the layer of water molecules holds to the oxygen atoms, and the water molecules are adsorbed on the crystal surfaces [1]. The sodium-saturated bentonite may cause a greater expansion than calcium-saturated bentonite, therefore it is important to obtain an appropriate ion exchange reaction in order to stabilize the clay.

As described earlier, smectite is the dominating component of bentonite, and the unique physical and chemical properties are depicted by bentonite due to this mineral. The smectite group minerals have similar structures, since majority of the clay minerals consists of

• Octahedral layer

• Tetrahedral layer

Various chemical compositions can be attained with different combinations of these two structures. The octahedral layer consists of two layers packed with oxygen atoms (O) or hydroxyl molecules (OH). An octahedral structure is built up of O- atoms or OH-molecules, and an aluminium atom (A) is placed within this structure, having the same distance to all O-atoms or OH-molecules, as shown in figure 3.1. The aluminium atom can be replaced by iron (Fe) or magnesium (Mg).

On the other hand, tetrahedral layer consists of a tetrahedral structure where O- atom or OH-molecule is placed in the four corners of the structure, and are surrounding by a silicon atom (Si) which is being placed in the gravitational center of the tetrahedral structure. Several of these structures can be tied together in a hexagonal pattern with an oxygen or hydroxyl corner, as can be seen in the figure3.1.

The tetrahedral structure is placed in such a manner that the top of the structure points in the upward direction, while bases are on the same plan.

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Figure 3.1: Structure of clay [12]

It is important to study the behaviour of the clay particles in drilling fluids as it affects important fluid properties such as viscosity, yield point and filter loss [30].

The property of the drilling fluid depends on the interaction between the clay crystals, which in turn are dependent on properties like pH and salt concentration of the solution [30]. In the following sections, four typical conditions for clay particles in the aqueous solution will be described, the conditions are also illustrated in figure 3.2.

Deflocculated system: Similar charges of the suspended particles in the solutions induce repulsive force between the particles and eventually the system becomes deflocculated [30]. The alkalinity of the solution increases this effect. As there are no ionic interactions between the particles in the deflocculated system, therefore the filter loss and yield point will be low.

Flocculated system: A fluid system is flocculated when the sum of repulsive forces and attracting forces between the particles are zero that is charge neutralization,

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the particles make a bond, either connected edge-to-edge or edge-to-surface. This takes place when clay crystals have positive charges on the edges. In a flocculated bentonite system, viscosity will increase and the filter loss will also increase.

Figure 3.2: Typical conditions for clay particles in drilling fluids [12]

Aggregated system: As the name indicates, in this system particles are bound together in aggregates. The aggregated bentonite system does not contain individual crystals or small groups of crystals, but crystals are packed together in aggregates. The montmorillonite is packed together in bonded sheets, and when the montmorillonite is hydrated, the sheets will separate and there will be a significant increase in the viscosity.

Dispersed system: A dispersed system is described as when all the aggregates are splits up into individual crystals or small group of crystals. When the system is dispersed, the charges at the edges can either be positive or negative, it depends on the pH value of the solution. A dispersed system can be either flocculating or deflocculating.

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3.2.2 Xanthan Gum-XG

Xanthan gum is polysaccharides and water soluble long chain anionic polymer. It is not usually compatible with cationic surfactants and polymers. Xanthan gum is used in drilling fluid for the control of viscosity and filtrate loss. As illustrated in figure 3.3, structurally, xanthan gum comprises of three-ring side chain and two-ring backbone, which consists of glucose that is identical to the ring structures in CMC.

The functional groups such as carbonyl and hydroxyl are attached to the side of the chain. This branching structure gives xanthan gum thixotropic properties. The polymer branches are connected by weak hydrogen bonding. During shearing, the bond will break easily and the fluid becomes thin. As drilling fluid is under static condition, the chains will retain their interaction by hydrogen bonding, and as a results viscosity returns back to the initial state [31].

Figure 3.3: Structure of Xanthan gum [31]

3.2.3 CMC

Carboxymethyl cellulose (CMC) is derived from cellulose, where carboxymethyl groups (-CH²-COOH) are bounded to the hydroxyl groups. As shown in figure 3.4, CMC has a linear structure and is a water soluble anionic polymer. In drilling fluids,